Rheological properties of whey protein isolate stabilized emulsions with pectin and guar gum

Dynamic oscillatory and steady-shear rheological tests were carried out to evaluate the rheological properties of whey protein isolate (WPI) stabilized emulsions with and without hydrocolloids (pectin and guar gum) at pH 7.0. Viscosity and also consistency index of emulsions increased with hydrocolloid concentration. At gamma = 20 s(-1), the value of viscosity of the emulsion with 0.5% (w/v) pectin was about fivefold higher than that of the emulsion without pectin. Flow curves were analyzed using power law model through a fitting procedure. Flow behaviour index of all emulsions except for containing 0.5% (w/v) guar gum was approximately in the range of 0.9-1.0, which corresponds to near-Newtonian behaviour. The shear thinning behaviour of emulsions containing 0.5% (w/w) guar gum was confirmed by flow behaviour index, n, of 0.396. Both storage (G') and loss modulus (GaEuro(3)) increased with an increase in frequency. Emulsions behaved like a liquid with GaEuro(3) > G' at lower frequencies; and like an elastic solid with G' > GaEuro(3) at higher frequencies. Effect of guar gum was more pronounced on dynamic properties. Phase angle values decreased from 89 to < 10A degrees with increasing frequency and indicated the viscoelasticity of WPI-stabilized emulsions with and without pectin/guar gum.